[Sync] Move thread checking into the ModelSafeWorker interface.

components/password_manager/sync/browser/password_model_worker.h

 // Copyright (c) 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_PASSWORD_MANAGER_SYNC_BROWSER_PASSWORD_MODEL_WORKER_H_
 #define COMPONENTS_PASSWORD_MANAGER_SYNC_BROWSER_PASSWORD_MODEL_WORKER_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "components/sync/engine/model_safe_worker.h"
 
 namespace password_manager {
 class PasswordStore;
 }
 
 namespace browser_sync {
 
 // A syncer::ModelSafeWorker for password models that accepts requests
 // from the syncapi that need to be fulfilled on the password thread,
 // which is the DB thread on Linux and Windows.
 class PasswordModelWorker : public syncer::ModelSafeWorker {
  public:
   PasswordModelWorker(
       const scoped_refptr<password_manager::PasswordStore>& password_store);
 
-  // syncer::ModelSafeWorker implementation. Called on syncapi SyncerThread.
+  // syncer::ModelSafeWorker implementation.
   syncer::ModelSafeGroup GetModelSafeGroup() override;
+  bool IsOnModelThread() override;
   void RequestStop() override;
 
  protected:
   syncer::SyncerError DoWorkAndWaitUntilDoneImpl(
       const syncer::WorkCallback& work) override;
 
  private:
   ~PasswordModelWorker() override;
 
   // |password_store_| is used on password thread but released on UI thread.
   // Protected by |password_store_lock_|.
   base::Lock password_store_lock_;
   scoped_refptr<password_manager::PasswordStore> password_store_;
   DISALLOW_COPY_AND_ASSIGN(PasswordModelWorker);
 };
 
 }  // namespace browser_sync
 
 #endif  // COMPONENTS_PASSWORD_MANAGER_SYNC_BROWSER_PASSWORD_MODEL_WORKER_H_